Granted, he lacks the warmth of Darth Vader or the charm of Jabba the Hutt. But Mitch McConnell, I have always thought, was a principled force for good in an evil, evil place.

Which is why it is so shocking to see the Senate minority leader knee-deep in the manure of slanderous lies being flung at the most conservative, most principled, and most electable candidate running in a primary a thousand miles away from his home state of Kentucky.

I have admired Mr. McConnell ever since he took the very lonely and unpopular — yet constitutionally scrupulous — stand against so-called campaign-finance “reform.” Sen. John McCain, the Republican failure from Arizona who gave us President Obama, supported these “reforms” because his only constituents are the Democratic media establishment and his own ego.

Also, having utterly disgraced himself and dishonored his family’s good name by jumping into bed with the Keating Five and costing taxpayers billions of dollars bailing out a corrupted industry, Mr. McCain had to spend the rest of his political career pretending to be clean, ethical, and above bribery. They call it “rebranding” around here.

When these “reforms” soon proved to be little more than an incumbent-protection program, they became very popular among the nest of politicians in office at that time. Mr. McConnell was among the lonely few who stood up to Mr. McCain and his egotistical campaign to restore his reputation by shredding the First Amendment.

In addition, Mr. McConnell has admirably led the notoriously un-leadable Senate Republican minority through some pretty dark days. His unblinking stare and pale, Skeletor visage have always inspired me to think that behind the mask is a ruthless and brilliant tactician, ever calculating and always in control — a good thing for conservatives to have in their Senate leader.

For these and other reasons, I have never understood the frothing bloodlust among so many good conservatives to see Mr. McConnell defeated in his Kentucky primary later this month.

But I’m not so sure any more.

Now roundly loathed by tea partiers nationwide as an underhanded insider, Mr. McConnell has his hands full with a challenge for his own party’s nomination. Then he must win re-election to the Senate at a time when his favorable ratings are dangerously low. And if he wants to go from being a nearly powerless minority leader to a majority leader who can actually stop the Obama agenda, he and Republicans need to pick up six seats held by Democrats.

Sounds like a pretty full plate, even for a brilliant and determined tactician like Mr. McConnell.

So why is it that he would be so obsessed with mucking up a Nebraska primary race where by all accounts the best, most conservative, and most electable Republican appears on the verge of winning? Polls show Ben Sasse close to grasping the nomination after running a clean, positive campaign laying out his vision for dismantling Obamacare.

From early on, Mr. McConnell has been squarely behind Nebraska politician Shane Osborn, who has run a relentlessly negative and dishonest campaign. In an attempt to smear Mr. Sasse, Mr. Osborn’s campaign has spun numerous fantasies about how Mr. Sasse doesn’t really want to repeal Obamacare. Really?

Then reporters at The Omaha World-Herald uncovered a bombshell. Mr. Osborn, a Navy veteran, conspired with some buddies in the Pentagon to forge a document on Navy letterhead in an effort to help out his political campaign. The forged document, summarizing classified information, was distributed to reporters.

Running a terrible and nasty campaign apparently doesn’t bother Mr. McConnell. He ordered the D.C. Republican establishment to get behind Mr. Osborn. Now a Political Action Committee formed by ex-McConnell staffers to advance Mr. McConnell’s interests has gotten in on the lying game.

It is hard to understand exactly why a brilliant tactician like Mr. McConnell would be so deeply involved in this campaign. Does Mr. McConnell feel threatened by Mr. Sasse? Does he secretly hate conservatives? Is he shilling for Obamacare?

Whatever the reason, when the only principles you stand for anymore are your own survival or some petty grievance, then your principles no longer have anything to do with the Constitution.

Charles Hurt can be reached at charleshurt@live.com and on Twitter @charleshurt.